Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 632	$ 793
Average amount outstanding (based on daily outstanding balances)	$ 487	$ 574
Weighted average interest rates	5.50%	4.80%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 14	$ 0
Average amount outstanding (based on daily outstanding balances)	$ 1	$ 0
Weighted average interest rates	5.50%	0.00%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 390	$ 349
Average amount outstanding (based on daily outstanding balances)	$ 255	$ 304
Weighted average interest rates	5.50%	4.80%